When he called the Doc he was told to attend at 6pm, "..and keep the evening free, it could be a long session"

What did the Doc mean by that? But trying to figure it out just made Tank's head hurt. And an order is an order.

So Tank made his way to Doc's office and arrived dead on 6pm. No-one was around, the whole building was quiet. He knocked on the office door, no answer. He opened the door and entered. A voice from an inner room called out. "Is that you Cadet Tank?"

"SIR, YES SIR" he answered.